The issues you're describing have nothing to do with server-client lag-- they're entirely graphical lag caused by your computer. I know because I have the same problems.

The good news is, you learn to deal with it and compensate. I got my own Titan EX clear just a few days ago by starting to move a second or so before the cast bar even appears on my screen. Titan is a 100% scripted fight, so all you need to do is know when WotL is going to happen in his rotation and react preemptively.